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Crop Protection 30 (2011) 587e591

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Crop Protection

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Evaluation of augmentative release of Zygogramma bicolorata Pallister(Coleoptera: Chrysomelidae) for biological control of Parthenium hysterophorus L.

Sushilkumar, Puja Ray*

National Research Centre for Weed Science, Maharajpur, Adhartal, Jabalpur (M.P.)-482004, India

a r t i c l e i n f o

Article history:Received 19 September 2008Received in revised form31 January 2011Accepted 2 February 2011

Keywords:AugmentationBiological controlParthenium hysterophorusZygogramma bicolorata

* Corresponding author. Tel.:þ917612405135 (Officfax: þ91 0761 2353129.

E-mail address: puja.ray@gmail.com (P. Ray).

0261-2194/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.cropro.2011.02.005

a b s t r a c t

Augmentative release of biocontrol agents has been largely successful for the management of insect pestsbut it has not been a common approach for weed management. Augmentation methods need to bedeveloped for weed management, especially for pernicious weeds like Parthenium hysterophorus L.,commonly known as pathenium or carrot weed. The leaf beetle Zygogramma bicolorata is a potentialbiocontrol agent of P. hysterophorus. Initial release of biocontrol agents is subject to uncertainties as towhether timely population built-up will take place in sufficient numbers. Several augmentative releasesmay be required to ensure early establishment of the biocontrol agents, for successful biological controlof noxious weeds including pathenium. We made augmentative releases of larvae or adults of Z. bico-lorata each to three sites, severely infested with pathenium at Jabalpur, India consecutively for a period ofthree years. Initially 10 larvae or adults per sq m were released in each plot, followed by a second, thirdand fourth release of 3, 1.5 and 1.5 larvae or adults per sq m at an intervals of 3, 7 and 14 days after thefirst augmentation. The pathenium at augmented sites were completely defoliated in 45 and 60 days bylarvae and adults respectively. There was also a reduction in the pathenium density and plant height inthe augmented sites as compared to the non-augmented sites. Over a period of 3 years augmentationresulted in a noteworthy negative effect on the weed.

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1. Introduction

Augmentation refers to the action taken to increase the pop-ulation of beneficial natural enemies to bring about effectivesuppression of pest population mostly by release of biocontrolagents in the areas of less abundance or where population build-upof the biological control agent occurs too late to cause appreciabledamage to the target pest. Augmentative biological control of pestinsects and mites using agents such as Trichogramma spp., Chrys-operla carnea (Stephens), Bracon spp., Pristhesancus plagipennis(Walker), etc, has been used extensively as a major crop protectiontool in several countries for control of a range of field crop pestsover large area (Grundy and Maetzer, 2002; Knutson and Teddlers,2002; Elzen and King, 1999; Khloptseva, 1991; Li, 1994; Greenberget al., 1996; Ables and Ridgway, 1981). But not much work has beendone on biological control of weeds by means of augmentativerelease of natural enemies, especially in India. Such intensifiedefforts were needed for the management of some of the noxiousweeds like Parthenium hysterophorus L.

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Parthenium is an annual herbwith a deeply penetrating tap rootsystem. It is a native of the area around the Gulf of Mexico andcentral South America (Navie et al., 1996). In the last sixty years ithas proliferated around the globe and has emerged as the seventhmost devastating weed in several tropical and subtropical regionsincluding Indiawithin last twodecades (Singh, 2001). It is estimatedthat about 35 million ha of land has been invaded by parthen-ium in India (Sushilkumar and Varshney, 2007). It is responsible forsevere health hazards to human and livestock besides being amajorthreat to native biodiversity and ecosystem (Mahadevappa, 1999;Sushilkumar, 2005; Shabbir and Bajwa, 2006.). The ability of par-thenium to grow in awide range of habitats, its large seed bank andits allelopathic potential renders its management very difficult(Sushilkumar and Saraswat, 1999; Dhileepan and Strathie, 2009).Among various control measures, the Mexican beetle, Zygogrammabicolorata Pallister (Coleoptera: Chrysomelidae) is a biologicalcontrol agent of parthenium (McFadyen, 1992; Dhileepan et al.,2000; Dhileepan, 2001). In the mid 1970’s it was acquired asa result of an exploratory faunal survey by the scientists of theDepartment of Lands and of the Commonwealth Institute of Bio-logical Control (CIBC, now IIBC) inNorth and SouthAmerica (McClayet al., 1995). Z. bicolorata adults measure 5e6 mm in length, andhave undulating dark brown lines running longitudinally over

Table 1Record of average temperature, humidity and rainfall during the study period.

Month Average Temp(�C)

AverageHumidity (%)

Average Rainfall (mm)

Max. Min. Max. Min.

June 38.1 27.2 58.0 37.0 141.4July 30.3 24.5 88.3 74.0 486.9August 28.8 23.9 91.0 77.0 423.3September 31.4 23.8 88.7 64.0 467.6October 30.9 18.8 87.3 45.3 28.8

Sushilkumar, P. Ray / Crop Protection 30 (2011) 587e591588

off-white background on the elytra. The female is capable of layingup to 45 eggs per day and 300 eggs per week. Adults lay eggs eithersingly or in groups on the leaves, flower heads, stem surfaces andterminal and axillary buds. The larvae emerge in 3e4 days and feedvoraciously on young leaves. They undergo four molts before thefully grown larvae burrow into the soil to pupate. The pupal stagelasts for 6e12 days. The whole life cycle takes 23e30 days. Thebeetles are multivoltine and there may be several generations peryear, depending on rainfall and food availability. Adult beetles canremain alive for a period of 122e271 days in male and 109e198days in females excluding the time span spent in diapause in thesoil during winter (Jayanth and Bali, 1993b; Sushilkumar, 2005).Both the adults and larvae of Z. bicolorata feed on partheniumleaves. After host specificity and biological studies (McClay, 1980;McFadyen, 1980; Jayanth and Nagarkatti, 1987; Jayanth and Bali,1993a, 1994b; Bhoopathi and Gautam, 2006) the beetles werereleased in various parts of theworld suffering parthenium invasionincluding India (McFadyen and McClay, 1981; Jayanth and Bali,1995). In central Queensland, Australia, Z. bicolorata caused91e100% defoliation, resulting in reductions in weed density by32e93%, plant height by 18e65%, plant biomass by 55e89%, flowerproduction by 75e100%, soil seed bank by 13e86% and seedlingemergence by 73e90% (Dhileepan et al., 2000). In India, Z. bicoloratawas released in Bangalore in 1984 and became abundant within3 years after introduction, resulting in a significant reduction inparthenium in localized areas (Jayanth and Bali, 1994a; Jayanth andVisalakshy, 1996).

Z. bicolorata has shown its biocontrol potential in different partsof the country ranging from negligible to excellent under differentfield conditions while use of herbicides against the weed hasalways given temporary but good results (Sushilkumar, 2005).Although indiscriminate use of synthetic herbicides has becomea major area of concern in recent years, yet we are unable todecrease our reliance on these chemicals owing to our need todecrease weed populations. Reliance on these chemicals can onlybe reduced by using biocontrol measures like augmentation of thenatural enemies of such weeds. If the Mexican beetle can be madeeffective by timely augmentation for control of parthenium, reli-ance on the herbicides can be decreased. The present work wasundertaken to evaluate the impact of augmentation of larvae andadults of Z. bicolorata for biological control of P. hysterophorus inJabalpur, India.

2. Materials and methods

2.1. Site selection

Nine parthenium infested sites were selected at differentlocalities of Jabalpur for the duration of three years. The selectedsites were at least 300 m away from each other and segregated byvarious landmarks. The selected sites were mostly areas that wereabandoned after human interference andwere not being used for atleast two years before commencement of the experiment. Thoughthe beetle had been present in various locations of Jabalpur, yet ithad not been recorded from these particular sites for at least twoyears before the start of the experiment. However attack by thebeetles from nearby locations cannot be ruled out during theexperiment. The selected sites had dense parthenium infestationsof 70e80 plants per sq m. The growth stage of the plants rangedfrom mostly pre-flowering to a few early-flowering. The averageheight of parthenium ranged from 30 to 65 cm (mean � SE of plantheight at different sites: 43.3 � 3.7 cm, 44.3 � 4.4 and 41.7 � 3.3 inadult, larval augmented sites and control sites respectively). Anaccount of climatic condition including average temperatures,humidities and annual rainfall is given in Table 1.

2.2. Mass rearing of Zygogramma bicolorata

In the summer season, from April to June under field conditions,the activity of the beetles remains low or almost nil except at a fewsites where sufficient moisture was available to sustain the devel-opment of the beetles. It has also been observed that after first rainsof the monsoon season, beetles take time to build-up sufficientpopulation to cause appreciable damage to parthenium. Thereforefor timely augmentation, rearing of beetles was attempted in 35small agro-net houses each of 6m2 area constructedwith a frame ofportable iron rods. Parthenium was grown in these chambers bybroadcasting of seeds to attain uniform distribution and height ofthe weed before releasing of Z. bicolorata for egg laying anddevelopment. These agro-net houses covered with using greenagricultural shade nets made of High Density Polyethylene (HDPE),giving 50% shade during the summer season. These chambers wereerected over one month old well- established and well- grownparthenium. Beetles were released inside these agro-net coveredplots for rearing. Densely growing lush green parthenium andmoisture enabled high population build-up of the beetles whichwere harvested by hand picking as and when required. Whenplants were completely defoliated by feeding of the beetle duringrearing, they were replaced from time to time by transplantingof small parthenium plants to enable continuous rearing of thebeetles during the season.

2.3. Augmentation of adults and larvae

Augmentation of Z. bicolorata was done by releasing adults orlarvae each at three sites. The remaining three sites were taken ascontrols. For each year, the beetles were released at the rate of 10adults or larvae per sq m. This was followed by release of larvae oradults in their respective sites on third day at the rate of 3 beetlesper sq m. Further releases of beetles were made on 7th and 14thday after initial augmentation at the rate of 1.5 beetles per sq m. Nobeetles were released in the control sites. In the larval augmentedsites, second and third instar larvae were released.

2.4. Monitoring of the augmented sites

Population built-up of the beetles was monitored by countingthe number of eggs, larvae or adults from 25 plants selectedrandomly from each site at intervals of 15 days after the first aug-mentative release until 100% defoliationwas caused to parthenium.The level of defoliationwasmonitored visually by assigning damagescores from 0 to 100%. Parthenium with complete defoliation fol-lowed by browning of shoots and stems were taken as plants with100% damage. The impact of augmentation on plant height wasmonitored by uprooting 25 plants from each site randomly andmeasuring their heights. This was done in the second week of Julyfor each of the three years of study when the age of the partheniumstand was about 20 days. Weed density at the sites was monitoredfor the three years from 2005 to 2007 in the second week of July by

Sushilkumar, P. Ray / Crop Protection 30 (2011) 587e591 589

counting the total number of plants per sq m at different spots ineach field. An attempt was made to measure plant height and plantdensity in 2008 following the first augmentative release in 2007.Plant height could not be monitored further in 2008 because ofabsence on enough plants in the augmented sites for the study.Therefore data for plant density only was acquired in 2008.

2.5. Statistical analysis

The experiment was conducted at the same selected sites forthree years. All the treatmentswere replicated thrice eachyear. Datawere subjected to analysis of variance (ANOVA) using the genstatstatistical programme. The treatment means were compared withleast significant difference (LSD) tests at the 5% significance level.

3. Results

3.1. Effect of augmentation on damage percentage of P.hysterophorus

Augmentation of Z. bicolorata caused substantial damage to theparthenium stand at all release sites (Fig. 1). By the 15th (F ¼ 97.66;df ¼ 8; 16 P ¼ 0.000) and 30th (F ¼ 350.3; df ¼ 8, 16; P ¼ 0.000) day,larval augmentation caused significantly greater damage comparedto the adult augmented sites. There was complete defoliation in thelarval augmented sites by the 45th day (F ¼ 454.54; df ¼ 8, 16;P ¼ 0.000) of augmentation. By the 60th day (F ¼ 1718.11; df ¼ 8, 16;P¼0.000), completedefoliationwasobtained in theadult augmentedsites while minor injury became visible in the control sites as well.

3.2. Effect of augmentation on population built-up of Z. bicolorata

Augmentative release of adults and larvae had a substantialinfluence on population built-up of Z. bicolorata (Fig. 2). In the adult

Fig. 1. Percentage damage caused by Z. bicolorata at augmented and control sites. Verticastatistically different at P ¼ 0.05.

augmented sites, therewas a significant difference in the number ofeggs, larvae and adults as compared to larval augmented sites andthe controls. By the 45th day (F ¼ 17.60; df ¼ 8, 64; P ¼ 0.000), nobeetle population could be recorded in the larval augmented sitesdue to 100% defoliation to the plants. A population of beetles beganto emerge in the control plots by the 45th day of augmentation.Though no beetles had been released, population built-up wasobserved from the middle of August.

3.3. Effect on plant height

It was observed that before augmentation, there was nosignificant difference between the plant height in augmented andcontrol sites. Augmentation of theMexican beetles had a significantinfluence on the plant height (Fig. 3). Two way analysis of the effectof plant height and the various treatments in the three yearsindicate that there was no significant difference among varioustreatments in various years but there was a significant difference inplant height in the augmented and control sites in each individualyear. There was no significant difference in the plant height in theadult augmented and the larval augmented sites in any of the years.Plant height in control sites was significantly greater as comparedto the plant height in the adult augmented and larval augmentedsites.

3.4. Effect on plant density

Augmentation had a significant negative impact on the plantdensity of parthenium (Fig. 3b). There was a significantly greaterincrease in parthenium density in the control sites from 2005(F¼ 0.21; df¼ 2, 6; P¼ 0.8) to 2008 (F¼ 112.95; df¼ 2, 6; P¼ 0.000)as compared to the marked decrease in the adult and larvalaugmented sites.

l bars indicate standard error of the mean. Mean marked with same letter(s) are not

Fig. 2. Abundance of Z. bicolorata in the augmented (adult and larval) and control sites.Vertical bars indicate standard error of the mean. Mean marked with same letter(s) arenot statistically different at P ¼ 0.05.

Fig. 3. Impact of augmentation of Zygogramma bicolorata (adult and larvae) and noaugmentation (control) on (a) plant height and (b) plant density of P. hysterophorus inthe 2nd week of July each year; age of parthenium about 20 days. Vertical bars indicatestandard error of mean. Mean marked with same letter(s) are not statistically differentat P ¼ 0.05 (ns indicate non-significant data).

Sushilkumar, P. Ray / Crop Protection 30 (2011) 587e591590

4. Discussion

In tropical countries like India, it is observed that after inocula-tive release of Z. bicolorata in an area, the insect colony takes about3e4 years to get established followed by parthenium suppression(Jayanth, 1987). But even after establishment, desirable control ofparthenium is not achieved timely due to slow population built-up

of the beetles. In India, such situations particularly emerge after pre-monsoon rains in JuneeJuly when parthenium germinates inabundance due to availability of moisture while beetle populationsremain low due to slowand intermittent emergence from diapause.The efficiency of Z. bicolorata as biocontrol agent faces a major setback due to diapause behaviour of the adult beetles. A largeproportion of the population of beetles is capable of enteringfacultative diapause over an extended period between July andDecember (Jayanth and Bali, 1993b) followed by emergence as theseasonwarms. Thus to compensate for this decrease inpopulation ofZ. bicolorata as a result of diapause, laboratory reared beetles ifreleased from time to time augmentatively in quick successionespecially in the early growth stage of parthenium, can havea substantial impact on weed stands and also in reducing the seedbank. Navie et al. (1998), while quantifying the effect of the stemgalling moth, Epiblema strenuana Walk (Lepidoptera: Tortricidae),another biological control agent for parthenium, on the growth andseed production of P. hysterophorus, observed that E. strenuanacaused no significant reduction in the height of P. hysterophorusplants if applied after 53 days; however, application of the insect at35 days led to plants that were significantly (34%) shorter than theplants without biocontrol. Thus early release of these biologicalcontrol agents is essential.

Sushilkumar, P. Ray / Crop Protection 30 (2011) 587e591 591

In parthenium, flowering usually commences 6e8 weeks aftergermination, and a fully grown plant produces about 25,000 floretsin its lifetime, with each inflorescence bearing four to five seeds(Dhileepan et al., 1996; Navie et al., 1996). Thus augmentativereleases followed by proper population build-up of the beetlesbefore this period could result in decreased seed production for thenext season. In the present study augmentative releases of theMexican beetles was done for three consecutive years on parthe-nium at the pre-flowering growth stage. This attempt helped tocause a large reduction in the plant density at the release siteprobably because of reduced seed production due to beetleherbivory before flowering. Defoliation caused by the beetles at theadult and larval augmented sites resulted in significant reductionsin plant height and density. Several authors (Jayanth and Bali,1994a; Jayanth and Visalakshy, 1996; Dhileepan, 2001) havereported 85e100% defoliation by Z. bicolorata resulting in reductionin parthenium density. Although larvae caused better damage thanthe adults, population built-up of the beetles was better in the siteswith adult augmentation.

We observed 100% defoliation of parthenium stand by the 45thand 60th day by larval and adult augmentation of Z. bicolorata.Dhiman and Bhargava (2005) reported 90% damage to partheniumstand by releasing 200 adult and 250 larvae in just 15 days underfield conditions. Such defoliation has immediate negative effect onplant performance and as a consequence affects the growth,reproduction and fitness (Prins and Verkaar, 1992).

At present the biocontrol campaign against parthenium hasresulted in only partial or inadequate control. The present studywas undertaken in limited areas but if such efforts can be made ona large scale involving an integrated approach the success ratecould be much higher.

Acknowledgement

We thank Dr. J.G. Varshney, Director, National Research Centrefor Weed Science, Jabalpur, India for providing the necessaryfacilities and encouragement. Financial support from IndianCouncil of Agricultural Research (ICAR), India is also acknowledged.

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